A variety of orthopaedic implants have previously been developed and are currently available for surgical implantation. A variety of metal materials, for example stainless steel or titanium, have been used for such implants. Often, where the implant is desired for bone replacement in a cranial or facial application, the implant is not generally of a standard size or configuration, and must be customized to fit the patient. In applications where such customization is advantageous, the use of metal materials, while desirable for their strength and biocompatibility, are less feasible due to the difficulty and expense of manufacture. Metal implants also obscure post-operative x-ray and MRI examination of patients, which is especially important when there has been tumor removal and it is desirable to assure no recurrence of the cancer. As a result, polymer materials have provided a desirable alternative for the manufacture of such custom implants.
One example of a custom polymer cranial implant is available from Stryker Corporation of Kalamazoo, Mich. The Stryker Custom Cranial Implant is derived from the patient's CT data, and converts the data into 3-D computer-generated images to build an anatomical model. The implant is a polymer material manufactured of 75% methylmethacrylate-styrene copolymer for strength, 15% polymethylmethacrylate (PMMA) for handling, and 10% barium sulfate for radio-opaqueness. An additional example of a craniofacial implant is offered by Porex Surgical Products Group of Newnan, Ga. The Medpor® implant is a biocompatible porous polyethylene material which allows tissue ingrowth. See www.porexsurgical.com. A still further example of a polymer implant for craniofacial applications is available from Osteopore International of Singapore. The Osteopore PCL scaffold bone filler is made from filaments of 3-D inter-woven bioresorbable polymer. This material has interconnected pores and is said to be cell tissue compatible.
While such prior art examples of polymer implants, particularly those used in craniofacial orthopaedic applications, have had desirable results, various disadvantages remain. In craniofacial implants, it may be advantageous to avoid adhesion and tissue ingrowth of the adjacent external and internal tissue, while at the same time encouraging bone ingrowth with the implant along the edges of the implant engaged with the skull. An implant of the prior art having all porous surfaces provides for boney ingrowth at the edge for stability but also has the disadvantage of allowing superior and inferior surfaces tissue ingrowth and/or adhesions. Prior art implants having smooth surfaces also failed to optimize boney fixation at the edge of the implant.